1. Field of the Invention
The present invention relates to a device for controlling personal protection means in a vehicle.
2. Description of the Related Art
The detection of front crashes in airbag control devices is in most cases based on acceleration sensors that sense in the longitudinal direction of the vehicle, situated for example centrally on the tunnel, but also at positions on the vehicle periphery, such as on the front end, or symmetrically on the two B pillars, etc. Here, in crashes against hard obstacles (e.g. a wall), higher acceleration signals are measured than in the case of crashes against soft obstacles at the same speed, in which restraint means or personal protection means nonetheless have to be activated. Therefore, it is an important requirement for triggering algorithms for personal protection means to be able to distinguish between fast crashes against soft obstacles (e.g. ODB crash, Euro NCAP) and slow crashes against a hard obstacle in which triggering should not take place (e.g. AZT insurance test).
Possibilities for distinguishing the two types of crash result from additional sensor mechanisms, such as for example up-front sensors, acceleration sensors that sense in the transverse direction of the vehicle, structure-borne sound sensors, predictive sensor systems, or through the use of the vehicle inherent speed. The disadvantages of these recognitions are their additional costs (sensor equipment), or, in the case of the use of the inherent speed, the disadvantage that the speed of the object crashed against is not taken into account, so that a false effective crash speed is assumed.
The triggering algorithms used here also use processed sensor signals, in addition to the measured acceleration signal. The intention and purpose of these processed features is, inter alia, to also include the history of the crash in the triggering features along with the currently measured acceleration value. Such processed features are for example a first or second acceleration integral having corresponding start and stop conditions that reproduce the decrease in speed or forward displacement of a freely flying mass during the crash, sliding window integrals without start-stop conditions that reproduce the decrease in speed over a fixed time range, acceleration signals low-pass-filtered in some other way, and/or integrals/window integrals over the magnitude, or a square of the magnitude, of pre-processed acceleration signals, which are a measure of the dynamic characteristic of the signal. All these features have in common that they can be continuously calculated during the course of the crash. In this way, the current feature value takes into account the overall history of the crash. For the crash classification and triggering decision of personal protection means, the current feature values are now continuously compared to threshold values, or feature combinations are compared to characteristic fields.
In Published German patent application document DE 10 2006 038 348 A1, a device is disclosed for crash classification having at least one sensor unit and an evaluation and control unit that evaluates the signals acquired by the at least one sensor unit for crash classification. Here, the at least one sensor unit is situated in the central region of the vehicle, and the signals acquired by the at least one sensor unit are evaluated by the evaluation and control unit taking into account known physical properties of the associated vehicle. The evaluation and control unit determines at least two temporal phases in the acquired signal curve, and infers a first type of crash, relating for example to an angular crash, an offset crash, and/or a crash against a pole, when the evaluation of the acquired signal curve yields the result that after a first temporal phase having at least one high signal amplitude that represents an impact of an outer region of a front of the vehicle against an obstacle, there occurs a second temporal phase having an essentially flat signal curve.